The present invention relates generally to the field of gas discharge tubes, and, more particularly, to a long-life deuterium lamp having enhanced heat dissipation capabilities.
Deuterium is a hydrogen isotope of mass 2, and is commonly identified by the symbol D. Deuterium occurs in nature as a diatomic molecule, and in compounds.
Deuterium arc lamps are well-known sources of light in the range of 190-400 nanometers. They are commonly used in various spectral analyzers, such as absorption detectors, spectral photometers, spectral scopes, and the like.
In general, deuterium lamps have an anode and a cathode arranged within an elongated tubular envelope made of a UV-transmitting glass or quartz. A focusing electrode is placed between the anode and the cathode. Deuterium gas is dosed into the envelope at a pressure of a few torr. In many cases, mechanical structure (e.g., anode, focusing electrode, and the like) is supported within the glass envelope on the distal ends(s) of one or more electrical conductors. Each conductor is generally in the form of a rod-like member having a large length-to-diameter ratio, and normally possesses sufficient strength to prevent or restrain axial movement of the mechanical structure within the envelope.
When a sufficient voltage is applied to the electrodes, a stream of electrons flow from the cathode to the anode. The electrons collide with the deuterium gas molecules and excite them to higher energy levels. When the molecules return to their ground state, energy is released in the form of photons in the UV range. The focusing electrode serves to constrict and intensify the discharge of the lamp to a diameter of one millimeter or smaller. The concentration of light by the focusing electrode makes it useful in the application of absorption detectors and similar instruments.
Details of prior art deuterium lamps are representatively shown in a catalog entitled xe2x80x9cDeuterium Lamps and Power Supplies for UV Analytical instrumentsxe2x80x9d, Imaging and Sensing Technology Corporation, Horseheads, N.Y. (undated), and in U.S. Pat. Nos. 4,433,265, 4,910,431 and 5,117,150. These references all appear to disclose different types of prior art deuterium lamps in which certain mechanical structure is cantilever-mounted on the distal end(s) of one or more electrical conductors. The aggregate disclosures of these various prior art references are hereby incorporated by reference.
Additional details of other known deuterium lamps are shown and described in U.S. Pat. Nos. 5,552,669, 5,684,363, 5,619,101, 5,633,563 and 5,698,945. Each of these patents is facially assigned to Hamamatsu Photonics K. K. However, one problem attendant such prior art designs is believed to stem from the relatively short life of the lamp. This problem is believed to originate in the difficulty in dissipating heat from the anode. In this regard, the ""669 patent appears to disclose an anode sandwiched between a discharge shielding plate and a support plate. Hence, it appears that it is difficult for heat to dissipate from the anode. The ""101 patent also shows the anode as being surrounded by an solid anode support member that tends to impede heat removal. The same is true of the ""563 patent. The ""363 patent appears to disclose an anode support plate to the rear of the anode. This anode support plate would itself impede heat transfer from the anode. Here again, the aggregate disclosures of these patents are hereby incorporated by reference with respect to the structure and operation of such prior art deuterium lamps and various physical implementations of same.
Accordingly, it would be generally desirable to provide an improved long-life deuterium lamp having enhanced heat transfer properties. It is thought that by facilitating the conveyance of heat away from the anode, the operational life of the lamp may be increased.
Generally, the life of a deuterium lamp is determined by its intensity. The lamp begins with an original intensity that degrades over time. When the intensity falls below 50% of its initial value, it is said to have reached the end of its useful life. This is an industry standard that is recognized by most manufacturers of deuterium lamps, even though the lamp may technically still retain some utility after its intensity has fallen below 50% of its initial value.
With parenthetical reference to the corresponding structure, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention provides an improved long-life lamp having enhanced heat transfer characteristics.
In one form, the improved lamp (20) has a gas-filled glass envelope (21); a cathode (22); an anode (23); electrical leads (24) sealingly penetrating the envelope and connected to the anode and cathode, respectively; a window-shielding electrode (25); a cathode-shielding electrode (26); a focusing electrode (28); and a ceramic support (29). In this form, the improvement broadly comprises the ceramic support having a front surface (66) facing toward the cathode, having a rear surface (68) facing away from the cathode, and wherein the anode is held against the support rear surface without substantially interfering with the radiation of heat therefrom in a rearward direction.
The anode may be held against the support by at least one fastener, such as a rivet, a bolt, a screw, or the like. The ceramic support may possibly be provided with a tapped hole to receive the threaded marginal end portion of such fastener. A ceramic shield may extend rearwardly from the rear surface of the ceramic support so as to surround the anode and to prevent arcing from the anode to the cathode. The anode is recessed within this peripheral shield, but is exposed rearwardly. The envelope may be filled with deuterium gas. The envelope may be formed of a UV-transmissive material.
The improvement may further comprise means for increasing the surface area of the anode on the rear thereof, to enhance thermal radiation therefrom. These means may include, but are not limited to, a plurality of fins, a radiator surface having an undulating cross-section, and/or a baffle so as to shape and direct the flow of gas within the envelope.
Accordingly, the general object of the invention is to provide an improved deuterium lamp.
Another object is to provide a deuterium lamp having improved heat-radiation characteristics from the rear of the anode.
Still another object is to provide a longer-life deuterium lamp.